x²y²-x²-y²+1 =x²(y²-1)-(y²-1)=(x²-1)(y²-1)=(x+1)(x-1)(y+1)(y-1)x²-2x-4y²-4y=x²-2x+1- (4y²+4y+1)=(x-1)²-(2y+1)²= [(x-1)+(2y+1)...